The present invention relates to a nematicide against pine wood nematodes (Bursaphelenchus xylophilus Mamiya and Kiyohara, etc.), and more particularly to an nematicide against pine wood nematodes containing a chlorinated hydroxystilbene. Further, the present invention relates to a method for synthesizing chlorinated hydroxystilbenes. Furthermore, the present invention relates to novel chlorinated hydroxystilbenes.
Pine wood nematodes have caused heavy damage, the dying of pine trees, in various places in Japan, which has posed a serious social problem. It has been well known that pine wood nematodes, fungivorous nematodes, enter pine wood tissues and propagate to cause pine trees to die.
The mechanism by which the pine wood nematodes cause the pine trees to die is considered as follows:
a) In the pine trees infected with the pine wood nematodes are produced toxins (phytoalexins) such as benzoic acid (1), catechol (2), dihydroconiferyl alcohol (3), 8-hydroxycarvotanacetone (4) and 10-hydroxyverbenone (5),
b) The nematodes secrete cellulase,
c) Tracheids of the pine trees are clogged with .alpha.-pinene and .beta.-pinene abnormally accumulated after the nematode infection, and
d) Toxins are secreted by molds which propagate in the pine trees after the nematode infection.
The pine wood nematodes are transmitted to the pine trees through injurious insects such as a pine sawyer (Monochamus alternatus Hope).
Previous methods for preventing the pine trees from dying by the pine wood nematodes mainly include (1) cutting down damaged trees to exterminate ova, pupae and adults present in the damaged trees before the pine sawyers carrying nematodes, which are directly responsible for the death of the pine trees, escape from the damaged trees, and (2) applying insecticides (sprinkling and cropdusting) for preventing maturing feeding after eclosion and escape of the pine sawyers. The insecticides used herein include organic phosphorus pesticides, NAC agents (1-naphthyl-N-methylcarbamate), PAP agents (ethyl dimethyl-dithiophosphorylphenylacetate), EDB agents (1,2-dibromoethyl), MPP agents (O,O-dimethyl-O-[3-methyl-4-(methylthio)phenyl] thiophosphate) and MEP agents (dimethyl(3-methyl-4-nitrophenyl) thiophosphate).
In addition to the above-mentioned insecticides for the pine sawyers, nematicides for directly exterminating the pine wood nematodes in the pine trees include a levamisole hydrochloride agent containing levamisole hydrochloride as a main insecticidal ingredient (trade name: "Century", Mitsubishi Petrochemical Co. Ltd., Japan), a mesulfenfos agent (trade name: "Nemanon", Nihon Bayer Agro Chem. K/K, Japan) and a morantel tartrate agent (trade name: "Greenguard", Fizer Pharmaceutical Inc., Japan).
The previous methods for exterminating the pine sawyers have the following problems:
(1) A great deal of labor is required.
(2) It is difficult to decide the suitable time of insecticide application because the time of emergence and escape of the pine sawyers differs from year to year.
(3) The effectiveness of the insecticides has become lowered.
(4) In order to achieve the exterminating effect in forests and fields, the dosage per unit area is required to be 10 times that generally used in agriculture.
(5) Social problems such as the remaining of the given insecticides in soil, the remaining in water systems and the effect on ecosystems such as surrounding animals and plants are encountered. The sufficient controlling effect can not be attained because of these problems.
(6) The previous insecticides for directly exterminating the pine wood nematodes in wood are effective, but have a problem in safety because of their toxicity.
The present inventor previously discovered that the nematicidal active substances against the pine wood nematodes were present in Pinus strobus, Pinus palustris and Pinus massoniana which were said to have a resistance to the pine wood nematodes, and found pinosylvin monomethyl ether (compound 1, see Table 3) which is a hydroxystilbene, as one of the active substances. The present inventor already filed an application for the nematicide containing this compound (UK Published Application No. GB 2263869 A; German Unexamined Patent Publication No. DE 4303346 A1; U.S. Pat. No. 5,314,693).